The present invention relates to bending large pipes by differentially heating the wall of the pipe within the region of the wall to be bent.
It is known to manufacture curved pipes in that a straight pipe is heated at the desired place of intended bending and is continuously bent along a circular line; see for example German published application No. 1,527,290. It is further known to prepare pipes for bending by means of a heating device being disposed behind a guiding and transport device and being movable to heat the pipe over a small cross-sectional region in each instant. In this case, the bending radius is determined by a swingable bending arm; see German published application No. 2,112,019.
It has also been proposed to dispose the heating device eccentrically in order to heat the pipe wall differentially. In this manner, it was attempted to reduce the weakening of the pipe wall at the outer radius of the curvature.
By means of the known process, it was not possible to obtain an optimum result with respect to the desired wall thickness. Therefore, pipes had to be used frequently which had to have a thicker wall at the outside in order to obtain the desired wall thickness in the finished pipe curvature.